In recent years, ink-jet recording systems have been applied to various printing fields such as photography, various forms of printing, marking, and special printing such as color filters due to its capability of forming images simply and inexpensively. Specifically, it has become possible to achieve image quality comparable to that of silver salt photography, by employing recording apparatuses which eject minute dots under control, inks which exhibit an enhanced color reproduction range as well as enhanced durability, and improved ejection adaptability, and exclusive sheets which exhibit markedly improved ink absorbability, color forming properties of color materials and surface glossiness. Enhancement of image quality of the current ink-jet recording system is achievable only by simultaneous improvement of all the recording apparatuses, inks and exclusive sheets.
However, ink-jet systems, which require special recording sheets, result in problems such as limitations of recording media as well as a higher cost of the foregoing recording media. As a result, a number of experiments have been conducted in which recording is carried out on image receiving media differing from such exclusive sheets, while employing various ink-jet systems. Specific examples include a phase change ink-jet system using a wax based ink which is solid at room temperature, a solvent based ink-jet system using an ink comprised of rapid drying organic solvents as a main component, and a UV ink-jet system in which after image recording, crosslinking is carried out employing ultraviolet (UV) radiation.
Of these, in recent years, the UV ink-jet system has received much attention due to its relatively low generation of unpleasant odors, rapid drying properties, and recording capability onto recording media exhibiting no ink absorbability. Ultraviolet radiation curing ink-jet inks are disclosed, for example, in Japanese Patent Publication No. 5-054667, Unexamined Japanese Patent Application Publication No. 6-200204, and Unexamined Japanese Patent Application Publication (under PCT Application) No. 2000-504778.
However, even though these inks are employed, it is very difficult to form high-definition images on each of the recording materials due to large differences of ink dot diameter after the ink deposition, depending on the type of recording materials and operation environment.
Specifically, UV radiation curable inks using a cationic polymerizable compound have been proposed (for, example, Patent Documents 1-3), however, these UV radiation curable inks have drawbacks which tend to be affected by molecular level moisture and oxygen inhibition action, and release of benzene, being toxic to the human body. In other words, in many cases, an active ray curable ink-jet ink composition using cationic polymerizable compounds described in foregoing Patent Documents 1-3 contains UVR6110 and UVR6105 produced by Dow Chemical Company, or CELLOXIDE 2021 produced by DAI CEL CHEMICAL INDUSTRIES, LTD. as a photopolymerizable compound, and thus, these compounds have drawbacks such as releasing harmful benzene, large fluctuation of ejection stability and curability under varying printing conditions (such as temperature and humidity), and wrinkling due to shrinkage while curing.
Patent Document 1: Unexamined Japanese Patent Application Publication (hereinafter, referred to as JP-A) No. 2001-220526
Patent Document 2: JP-A 2002-188025
Patent Document 3: JP-A 2002-317139